It is important for a wind turbine to have advance knowledge of the condition of the wind which will shortly arrive at the turbine. Such advanced knowledge gives the turbine controller sufficient time to adjust operating parameters such as blade pitch angle or rotor speed to match the oncoming conditions. This may be done for a variety of reasons. At lower wind speeds, it is important to adjust the turbine to maximise the energy extracted from the wind. At higher wind speeds it is important to adjust turbine parameters to avoid operations under conditions which might lead to damage. Damage might be caused by a rare extreme event or by cumulative events which reduce the fatigue lifetime of wind turbine components such as the gearbox and the blades.
A number of proposals have been made for determining advance wind conditions. Generally, these include the use of sensors placed on the turbine which observe the upstream wind. An example is shown in EP-A-0970308 which discloses the use of a Lidar or similar remote sensing apparatus mounted on the nacelle of the wind turbine and sensing wind conditions several rotor diameters upstream of the turbine. Based on the sensed conditions, the turbine controller or wind park controller can instruct an individual turbine, or a group of turbines, to change their operating parameters before the sensed wind arrives at the turbine or turbines.
Of particular importance to a wind turbine operator is the ability to detect extreme gusts of wind. Although these may be short lived, they have the potential to cause serious damage to the wind turbine. Although Lidar may be used for gust detections it is not always appropriate. For example Lidar devices are very expensive and may not be considered cost effective by a wind park operator.
We have appreciated that either as an alternative or in addition to remote sensing techniques such as the Lidar of EP-A-0970308, it is desirable to be able to estimate the risk of an extreme gust occurring without the use of expensive additional equipment.